In a substation for electric railcars, when an emergency has occurred while an electric vehicle is running on a railroad line, for example, when a relay has detected an occurrence of an electrical accident such as electric leakage or ground fault, or when an emergency alarm (e.g., an emergency warning signal) has been given due to, for example, entry by someone into a track including a power-feed rail, it is necessary for the substation to immediately stop power feeding to cut off power to the power-feed rail.
In the case of a substation of a DC feeding system, it is known that, due to a rectifying operation by a rectifier of the substation, a ripple (a pulsating current) is superimposed on a DC feeding voltage sent from the substation to a power-feed rail. Accordingly, as disclosed in Patent Literature 1, cutting off of the power sent from the substation can be detected based on disappearance of the ripple superimposed on the DC feeding voltage. It should be noted that Patent Literature 2 discloses a power cut-off detection method applied to an AC electric railcar configured to stop regenerative braking when detecting cutting off of power feeding.